Ball grid array technology is increasingly employed in the manufacture of high performance semiconductor components requiring a high input/output capability. A ball grid array semiconductor component includes external contacts in the form of balls arranged in a dense grid pattern (e.g., rows and columns). Exemplary ball grid array semiconductor components include BGA packages, chip scale packages, and bumped bare dice.
The balls in the ball grid array can have different shapes, such as spherical, hemispherical, or dome. Typically the balls comprise solder, which permits the semiconductor components to be surface mounted, or alternately flip chip mounted, to a mating component such as a printed circuit board.
Recent developments in ball grid array technology permit the balls to be made smaller and with tighter pitches. For example, for fine ball grid array (FGBA) components, the balls can have a diameter as small as about 0.127 mm (0.005 inch), and a center to center pitch as small as about 0.228 mm (0.008 inch). As the balls become smaller and closer, it becomes more difficult to make electrical connections with the balls for testing and for surface mounting the components in the fabrication of electronic assemblies.
For testing applications, sockets are typically employed to hold the components, and to make the temporary electrical connections with the contact balls on the components. The socket then interfaces with a test board, or other substrate, in electrical communication with test circuitry.
FIGS. 1A and 1B illustrates a prior art component 10 that includes contact balls 12. As used herein the term "contact balls" refers to external contacts on the component 10 in electrical communication with integrated circuits or other electrical elements contained on the component 10. The contact balls 12 can have any conventional shape that provides a raised contact surface. By way of example, representative shapes include spherical, hemispherical, dome, bump and conical. In addition, the contact balls 12 have a diameter "D" and a pitch "P". A representative range for the diameter D can be from about 0.127 mm (0.005 inch) to 0.762 mm (0.030 inch). A representative range for the pitch P can be from about 0.228 mm (0.008 inch) to 2.0 mm (0.078 inch).
FIG. 2A illustrates a prior art test system 14 for testing the component 10. The test system 14 includes multiple sockets 16 mounted to test sites 22 on a test board 18. Each socket 16 is designed to hold a component 10.
As shown in FIG. 2B, the test sites 22 on the socket 16 include contacts 24 in electrical communication with test circuitry 20. The contacts 24 are adapted to make temporary electrical connections with the contact balls 12 on the component 10. In the embodiment illustrated in FIG. 2B the contacts 24 are mounted in openings 28 in the socket 16 and include y-shaped segments 26 that physically and electrically engage the contact balls 12. A force applying mechanism (not shown) associated with the socket 16 presses the component 10 against the contacts 24 with a force F. This permits native oxide layers on the contact balls 12 to be penetrated by the y-shaped segments 26. In addition to the y-shaped segments 26, the contacts 24 on the socket 16 also include terminal segments 30 that plug into electrical connectors 32 in the test board 18. As shown in FIG. 2C, the pitch P of the contacts 24 matches the pitch P (FIG. 1B) of the contact balls 12. As shown in FIG. 2D, the pitch P of the terminal segments 30 of the contacts 24 also matches the pitch P (FIG. 1B) of the contact balls 12. This type of contact 24 is sometimes described as a "straight through" contact.
Alternately, as shown in FIGS. 2E and 2F, another type of contact 24A is adapted to exert a force F on the contact balls 12. As shown in FIG. 2E, an opening 28A receives the contact ball 12 with the contact 24A in an unactuated position with a zero insertion force. As shown in FIG. 2F, actuation of the contact 24A presses the contact 24A against the contact ball 12 with a force F. The contact 24A can be constructed with a mechanical lever or rocker as is known in the art. This type of contact 24A is adapted to exert a wiping action on the contact ball 12 which breaks through native oxide layers.
One problem with the conventional socket 16 is that it is difficult to accommodate contact balls 12 having a pitch of less than about 0.65 mm. Specifically, the contacts 24 (or 24A) cannot be made as small, or as close, as the contact balls 12. This is especially true with sockets having "straight through" contacts 24. Also, components that mate with the socket 16, such as the test board 18, must include mating electrical connectors 32 for the contacts 24 (or 24A). The mating electrical connectors 32 may require more space to fabricate than the contacts 24 (or 24A), making fabrication of the test board 18 difficult.
Another problem with the conventional socket 16 is that the contacts 24 (or 24A) can only make electrical connections with one size and pitch of contact balls 12. Often times a component 10 will be initially manufactured with contact balls 12 having a relatively large size (e.g., 0.40 mm) and pitch (e.g., 1.0 mm). However, due to design and fabrication process improvements, the size and pitch of the contact balls 12 will shrink. This requires that the socket 16 be redesigned and replaced each time the component 10 changes. This type of socket 16 is expensive to make, and becomes more expensive as the size and pitch of the contact balls 12 decreases. The test boards 18 for the sockets 16 must also be redesigned to accommodate the replacement sockets. In general, redesign and replacement of the sockets and test boards represents a significant expense for semiconductor manufacturers.
The present invention is directed to an interposer which configures test sockets for testing components having different sizes and pitches of contact balls. In addition, the interposer permits test sockets to be constructed with external contacts having a pitch that is greater than a pitch of the contact balls on the component. The interposer can also be utilized in assembly applications for modifying electronic assemblies to accommodate components having different contact balls.